Other versions exist on this site from various publications. This one is from the Radio Electronics Experimenter from 1990. The bargraph circuit uses the UAA170.
8E) This siren was found in a 1989 documentation. It uses only transistors and includes two power...
We found this circuit, which appears with variations on this site, in a European documentation from the...
The operational amplifier used in this configuration is of an uncommon type today. The circuit can be...